A visual explanation of this phenomenon. Blower surge is caused by the air moving past the butterflies on the injector hat. The butterflies get sucked shut which causes the engine RPM to slow down enough for the butterflies to open back up and increase the engine RPM until they get sucked shut and again and the cycle continues. With a mechanical fuel pump, fuel flow is directly related to engine RPM as well. If you physically open the throttle the surge is eliminated because there is enough room to let the air past the butterflies without cycling them open and closed. Steve Swacker’s blown alcohol 454 big block Chevy.